For typical energy efficient office buildings the following energy concepts are studied and the role of the building envelope in each of the concepts is described with special focus on:

• Passive solar design (Thermal insulation of the building envelope, windows/glazing type, size and orientation)

• Climate adapted design (Air tightness of the building envelope, efficiency of heat recovery system)

• Active solar design (BIPV, Solar thermal collector)

The total energy consumption is simulated for four different construction standards and the results are compared using dynamic building simulation software SQIAC [2]. First, the Old Norwegian standard from 1997 was taken and the resulting energy savings of special construction details is shown. Then, the resulting energy savings of the New Norwegian regulations (TEK 2007) are calculated. After that, the passive house standard (PH) is applied to a typical office building and the resulting energy savings are shown. Finally, possibilities for on-site renewable energy production to reach zero net energy buildings are explored.

In this respect it was interesting to estimate the uncertainty in the input parameters. A sensitivity analysis of eight different design parameters for an office building has been carried out and detailed results have been reported [6,7]. The technologies suggested for upgrading the buildings from one category to another were determined by sensitivity analysis and were summarized. The New TEK07 tightens the requirements for U-values of the building envelope and air tightness and requires setting the cooling set point temperature to 22°C which increases the cooling energy consumption. Therefore, two low energy categories were simulated; one with set point temperature set to 22°C, the other with set point temperature set to 26°C.

Table 1. Geometry of buildings model floors length width height floor area facade area floor area A/V [-] [m] [m] [m] [m2] [m2] [m2] [m-1] 1a 2 116.0 27.15 7 3149 2004 6299 0,377 1b 2 174.0 18.10 7 3149 2689 6299 0,408 2a 3 116.0 18.10 10.5 2100 2816 6299 0,318 2b 3 77.34 27.15 10.5 2100 2194 6299 0,290 3a 4 87.0 18.10 14 1575 2943 6299 0,276 3b 4 58.0 27.15 14 1575 2384 6299 0,251 4a 5 69.6 18.10 17.5 1260 3070 6299 0,254 4b 5 46.4 27.15 17.5 1260 2574 6299 0,231

The building geometry for the buildings PH+ concept was changed in order to identify the building geometry with the minimum energy consumption and maximum roof and facade area for energy production. Electricity production from PV cells (with overall efficiency of 11%) and thermal energy production from solar thermal collectors (with overall efficiency of 56%) were considered. Annual solar flux on surfaces of the building were determined from SCIAQ [2].

The geometry of the different cases is described in Table 1. All building models have the same total heated floor area of 6299m2 while the building height has been altered between 2 and 5 floors in order to study the sensitivity of the A/V ratio.

2. Results

2.1. Sensitivity of design parameter

In order to identify the uncertainty of design input parameters an OAT sensitivity analysis was done for TEK07 building standard [9]. Figure 2 shows the scatter plots for four design parameters together with their regression curves. They show that most design parameters are sensitive to changes except the orientation of the building. It can further be seen that the parameters have different sensitivity towards heating and cooling energy consumption.

• While a decrease in air leakage results in a reduction in heating energy consumption it increases (to a smaller degree) the energy consumption for cooling.

• A decrease of the U-value of the windows results in a reduction of heating but an increase in cooling energy consumption.

• A decrease of the window-to-floor-ratio (WFR) results in a reduction of heating and cooling energy consumption.

• An increase of the efficiency of heat recovery system results in a reduction of heating energy consumption.

• A decrease of the equipment load results in an increase of heating but a reduction in cooling energy consumption.

• A decrease of the lighting load results in an increase of heating but a reduction in cooling energy consumption.

2.2.

An increase of the cooling set point temperature results in a reduction of heating and cooling energy consumption

Energy concepts

Different energy concepts have been developed that apply results from the sensitivity analysis in order to reduce total energy consumption of the building. They are described as follows:

The energy concept of LE-OLD was based on the following measures:

• Increase in air tightness to n50 = 1.5 ach (from n50 = 4.29 ach)

• Reduction of windows area to WFR = 0.131 (from WFR = 0.1745)

• Installation of an effective external shading device with Fs = 0.5 (compared to no shading device with Fs = 1)

• Introduction of a heating set back temperature of Th = 20°C

• Installation of efficient lighting and equipment with ql = qe = 10 W/m2

The energy concept of LE-NEW was based on TEK07 with the following measures:

• Increase in air tightness to n50 = 1 ach (from n50 = 1.5 ach)

• Reduction of windows area to WFR = 0.131 (from WFR = 0.1745)

• Increase in efficiency of heat recovery system to ny = 0.85 (from ny = 0.7)

The energy concept of passive house was based TEK07 with the following measures:

• Increase in air tightness to n50 = 0.6 ach (from n50 = 1.5 ach)

• Increase in efficiency of heat recovery system to ny = 0.85 (from ny = 0.7)

The energy concept of PH+ was based on passive house with the following measures:

• Reduced installed power of lighting by reasonable placing of lights

• Control based on time, motion sensors, and daylight sensors

• In the calculation model these measures have been implemented by reducing the lighting load to ql = 6 W/m2 (from ql = 8 W/m2)

• Use of LCD-flat screens. laptops and others (printers. scanners. copy machines) with high energy efficiency led to qe = 5 W/m2 (from qe = 11 W/m2)

Figure 3 gives the results of calculations for an office building. It can be seen that heating energy consumption can be significantly reduced. The New low-energy concept is very sensitive to cooling set point temperature. For LE-NEW with a cooling set point temperature of 22°C there is more energy consumed for cooling than for heating. LE-NEW with a cooling set point temperature of 26°C there is not a large difference to the passive house concept (PH). The PH+ concept exceeds the allowed maximum of 15 kWh/(m2a). Improvements could be reached by applying windows with a lower U-value (see sensitivity analysis in previous section).

LE-OLD LE-NEW*

LE-NEW**

Passive house (PH)

Passive house (PH+)